Stretch blow molding (SBM) machinery is designed to rapidly mold packaging and containers for beverages, dairy products, medications and other products from molded preforms and thin sheets. See for example; U.S. Pat. No. 3,775,524; U.S. Pat. No. 4,145,392; U.S. Pat. No. 4,668,729; EP 870,593; EP 1,265,736; EP 1,679,178A; JP 09-194,543; WO 96/08,356A; WO 2005/074,428A; WO 2005/077,642; WO 2006/040,627A; WO 2006/040,631A; and WO 2007/060,529A.
One objective of the SBM process is to obtain the highest possible packaging efficiency ratio, i.e., milliliters of contents per weight of container in grams (ml contents/g container), through optimized wall thickness distribution and container top-load while meeting the processing window requirements at the shortest cycle time. Conventional thermoforming (TF) high impact polystyrene (HIPS) grades demonstrate through experimentation to have sufficient suitability for the compression blow forming (CBF) process. However HIPS has limitations with respect to: environmental stress crack resistance (ESCR), low temperature toughness, and water vapor transmission rate (WVTR). The substitution of HDPE for HIPS can overcome these drawbacks but due to the semi-crystalline structure of HDPE and its limited melt strength, it has a very narrow processing window which makes it an impractical polymer choice for commercial/industrial manufacturing.